<!DOCTYPE HTML>
<html>
<body>
<iframe src="data:application/vnd.mozilla.xul+xml,<?xml version='1.0' encoding='UTF-8'?><window xmlns='http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul' style='background:yellow'></window>"
        style="position:absolute; left:100px; top:100px; width:300px; height:300px; border:1px solid black;">
</iframe>
</body>
</html>
